The present invention relates to a pattern formation method for use in fabrication processing or the like for a semiconductor integrated circuit device.
In the fabrication processing for a semiconductor integrated circuit device, the size of a resist pattern (pattern width) formed by lithography technique is required to be further refined in accordance with increase in the degree of integration of semiconductor integrated circuits.
Also, the dielectric constant of an insulating film is desired to be further lowered in accordance with improved performance of semiconductor devices. Therefore, use of a low dielectric insulating film that has a lower dielectric constant than a generally used silicon oxide film, such as an insulating film having pores or including an organic material, has been proposed.
Now, a conventional pattern formation method will be described with reference to FIGS. 8A through 8C, 9A and 9B.
First, a chemically amplified resist material having the following composition is prepared:
Base polymer: poly((methoxymethyl acrylate) −  2 g(γ-butyrolactone methacrylate))(wherein methoxymethyl acrylate:γ-butyrolactonemethacrylate = 70 mol %:30 mol %)Acid generator: triphenylsulfonium triflate0.04 gSolvent: propylene glycol monomethyl ether acetate  20 g
Next, as shown in FIG. 8A, an organic polymer made of aromatic hydrocarbon including no fluorine (for example, SiLK manufactured by Hitachi Chemical Co., Ltd. (with a dielectric constant of 2.65)) is deposited on a substrate 1 so as to form a low dielectric insulating film 2 corresponding to an underlying film. Thereafter, while annealing the substrate 1 at a temperature of 90° C., gas-phase hexamethyldisilazane 3 is supplied onto the surface of the low dielectric insulating film 2 for 90 seconds, so as to form a molecular layer 4 of trimethylsilyl groups on the low dielectric insulating film 2.
Next, as shown in FIG. 8B, the chemically amplified resist material having the aforementioned composition is applied over the low dielectric insulating film 2 having the molecular layer 4 thereon, so as to form a resist film 5 with a thickness of 0.4 μm.
Next, as shown in FIG. 8C, pattern exposure is carried out by irradiating the resist film 5 with ArF excimer laser 7 emitted from an ArF laser exposure machine (with numerical aperture NA of 0.60) through a photomask 6 having a desired pattern.
Then, as shown in FIG. 9A, the resist film 5 is subjected to post-exposure bake (PEB) by annealing the substrate 1 at a temperature of 105° C. for 90 seconds. Thus, an exposed portion 5a of the resist film 5 becomes soluble in an alkaline developer because an acid is generated from the acid generator therein while an unexposed portion 5b of the resist film 5 remains insoluble in an alkaline developer because no acid is generated from the acid generator therein.
Next, after the pattern exposure, the resist film 5 is developed with an alkaline developer of a 2.38 wt % tetramethylammonium hydroxide aqueous solution for 60 seconds and is then rinsed with pure water for 60 seconds. Thereafter, the resultant resist film 5 is dried. Thus, a resist pattern 8 with a pattern width of 0.11 μm is formed from the unexposed portion 5b of the resist film 5 as shown in FIG. 9B.
The cross-sectional shape of the resist pattern 8 has, however, a footing shape as shown in FIG. 9B, and thus, the pattern shape is defective.
The conventional pattern formation method shown in FIGS. 8A through 8C, 9A and 9B is employed for forming a positive resist pattern 8. In the case where a negative resist pattern is formed, the resultant resist pattern has an undercut cross-sectional shape, and the pattern shape is also defective.
When a resist pattern in a defective pattern shape is used for etching a film to be etched, the shape of the resultant pattern of the etched film is also defective, which disadvantageously lowers the yield of semiconductor devices.